Old mum good, old dad bad

Older dads are more likely to father children with reduced cognitive abilities, and their sperm is probably to blame.

A study by researchers from the Queensland Brain Institute published in today’s Plos Medicine has found that advanced paternal age is associated with a poorer performance on standard cognitive tests than average.

By contrast, children with older mothers performed better on the tests, which include the Stanford Binet intelligence scale, tests for general intelligence in young children and those assessing conceptual and perceptual motor ability.

It is thought by some that children of older mothers have improved cognitive abilities as these mothers are able to provide a more nurturing or enriching environment, or the fact that older mothers have higher socio-economic status.

Several studies have found a correlation between advanced paternal age and neurodevelopmental disorders, including autism and dyslexia, and neuropsychiatric conditions such as schizophrenia. The link between older mothers and increased rates of Down syndrome are very well established.

Not much research has been done on cognitive abilities, however. Now, the QBI researchers, led by Professor John McGrath, have taken a closer look at a large birth cohort – the US Collaborative Perinatal Project – from which they studied data on 33,437 singletons.

They found a statistically significant association between advanced paternal age and inferior performance on all neurocognitive tests, except for a motor score. They also found statistically significant associations between advanced maternal age and superior performance on all measures.

The researchers point out that the cohort was only tested up to the age of seven years, and there is the possibility that cognitive ability improved as the children get older.

However, they also say mechanisms related to the development of the male germline warrant consideration. The older the father the older the sperm, and much genomic research has shown that older sperm is more likely to develop de novo mutations through epigenetic changes.

“A woman’s eggs are formed largely while she is herself in the womb, but sperm-making cells divide throughout a man’s lifetime, increasing the chance of mutations in sperm,” they write.

Oocytes have a limited lifespan but sperm lives for much longer. By the age of 20, a man’s progenitor sperm cells have undergone approximately 150 divisions, they write.

“By the age of 50, this number is 840. Thus, the chance of copy error mutations increases with age in males more dramatically than for females.”

Further work needs to be done to confirm the findings, they conclude.